Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The ionized gas supplied to the emitter tip of a gas field ionization ion
source is cooled and purified to enable supplying a reliable and stable
ion beam. Impurities contained in the ionized gas destabilize the field
ionization ion source. The invention is configured to include a first
heat exchanger thermally connected to a part of the field ionization ion
source, a cryocooler capable of cooling a second gas line and a cold
head, the second gas line being connected to the first heat exchanger and
circulating a refrigerant, and a second heat exchanger that cools the
first and second gas lines and is connected to the cold head.

Claims:

1. A charged particle microscope that has a field ionization ion source,
the microscope comprising: an emitter tip having a needle-like apex; an
ionization chamber having the emitter tip inside the chamber; a first
heat exchanger connected to a part of the ionization chamber via a
cooling conductor, a cryocooler having a second heat exchanger, a first
gas line that supplies a gas to the ionization chamber via the second
heat exchanger; and a second gas line thermally connected to the first
heat exchanger and the second heat exchanger.

2. The charged particle microscope according to claim 1, wherein the
second heat exchanger is thermally connected to a vacuum chamber
retaining a gas molecule supplied to the first gas line, and wherein a
mechanism by which a gas flow rate through the first gas line is adjusted
is provided on a path between the vacuum chamber and the first gas line.

3. The charged particle microscope according to claim 2, wherein the gas
running through the second gas line is partially suppliable to the
ionization chamber.

4. The charged particle microscope according to claim 1, comprising: a
first device mount that holds the field ionization ion source, a sample
holder for holding a sample, and a lens group for converging an ion beam;
and an antivibration mechanism that reduces a vibration of the device
mount, wherein the cryocooler is supported by a second device mount
separately provided from the device mount.

5. The charged particle microscope according to claim 1, comprising a
pipe that vacuum insulates the first gas line and the second gas line,
wherein an outer wall of the first gas line and an outer wall of the
second gas line are partially in contact with each other inside the pipe.

6. The charged particle microscope according to claim 1, wherein the
cryocooler is a Gifford-McMahon cryocooler or a pulse tube cryocooler.

7. The charged particle microscope according to claim 1, wherein the
cryocooler has a capacity to cool a cold head to a temperature of 70 K or
less.

8. The charged particle microscope according to claim 1, wherein the
cryocooler has a container capable of retaining liquid nitrogen, and
wherein the liquid nitrogen retained in the container is solidifiable
upon lowering a pressure inside the container.

9. The charged particle microscope according to claim 1, wherein the gas
supplied to the ionization chamber is helium gas.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a charged particle microscope.

BACKGROUND ART

[0002] Observation of a sample surface structure is possible through
detection of the secondary electron charged particles released by the
sample scanned and irradiated with electrons. This is called scanning
electron microscope (hereinafter, "SEM"). Another way to observe a sample
surface structure is through detection of the secondary charged particles
released by the sample scanned and irradiated with an ion beam. This is
called scanning ion microscope (hereinafter, "SIM").

[0003] Such surface observation preferably uses light ion species such as
hydrogen and helium. Lighter ion species are preferred for their weak
sputtering effect, minimizing the damage to a sample surface. Another
characteristic of these ion beams is the higher sensitivity to the
information of a sample surface than that of electron beams. Hydrogen and
helium ions are more sensitive because the excitation region of secondary
charged particles upon entry of these ions into a sample surface occurs
by being localized more toward the sample surface than the excitation
region occurring upon electron beam irradiation. Another disadvantage of
electron beams is that the wave property of electrons cannot be ignored,
and the diffraction effect causes aberration. The ion beams, on the other
hand, are heavier than electrons, and the diffraction effect is
negligible.

[0004] Information that reflects the inner structure of a sample can be
obtained by detecting ions that passed through the sample irradiated with
ion beams. This is called transmission ion microscopy. Lighter ion
species such as hydrogen and helium are particularly preferred for
observation because a large proportion of these ions passes through a
sample upon irradiation of the sample with these ions.

[0005] On the other hand, heavy ion species such as oxygen, nitrogen,
argon, krypton, xenon, gallium, and indium are preferred for the working
of a sample because these ions can have a sputtering effect on the
irradiated sample. A focused ion beam device using a liquid metal ion
source represents a known specific example of ion beam processing
devices.

[0006] A gas field ionization ion source is the preferred ion source for
ion microscopy. Ina gas field ionization ion source, high voltage is
applied to the metal emitter tip having an apex curvature radius of about
100 nm or less to concentrate an electric field at the apex, and a gas
(ionized gas) is introduced near the apex to ionize the gas molecules in
the field and obtain an ion beam. A gas field ionization ion source can
generate an ion beam of a narrow energy width. Further, the small size of
the ion source enables generating a fine ion beam.

[0007] Ion microscopy requires producing an ion beam of a large current
density on a sample to obtain a sample image with little noise. This
requires increasing the ion emission angle current density of the field
ionization ion source. The ion emission angle current density can be
increased by increasing the density of the ionized gas in the vicinity of
the emitter tip.

[0008] Cooling the emitter tip to extreme low temperatures lowers the
energy of the ionized gas molecules that collided with the emitter tip,
and the ionized gas molecules aggregate and increase their density. The
pressure of the ionized gas introduced near the emitter tip also can be
increased. However, problems occur when the pressure of the introduced
gas is 1 Pa or higher. Specifically, the ion beam neutralizes as it
collides with the ionized gas, and the ion beam current decreases, or
undergoes a glow discharge. A known solution to these problems is to
restrict the gas ionization region with a projection of several atoms
formed at the apex of the emitter tip, and improve ion emission angle
current density by efficiently ionizing the limited supply of ionized
gas.

[0009] Specifically, PTL 1 discloses improving ion source characteristics
with a fine protrusion formed at the apex of the emitter tip.

[0010] PTL 2 discloses a charged particle microscope that enables
high-resolution sample observation with a compact ion irradiation system
that has a reduced ion optical length to reduce the amplitude of the
relative vibrations of the emitter tip and the sample.

[0011] PTL 3 discloses an ion microscope. The main body of the ion
microscope is independently installed from a cryocooler for cooling a gas
field ionization ion source, and the mechanical vibration of the
cryocooler that propagates to the gas field ionization ion source is
reduced by the provision of a refrigerant circulation circuit cooling
mechanism that circulates a refrigerant between the gas field ionization
ion source and the cryocooler. In this way, the ion microscope can
improve the brightness of the gas field ionization ion source while
ensuring the ion beam convergence.

CITATION LIST

Patent Literature

[0012] PTL 1: JP-A-58-85242

[0013] PTL 2: WO2011/055521

[0014] PTL 3:
JP-A-2011-14245

SUMMARY OF INVENTION

Technical Problem

[0015] The gas field ionization ion source with a projection of several
atoms formed at the apex of the emitter tip has the following problems.

[0016] The gas field ionization ion source requires introducing an ionized
gas near the emitter tip, as described above. Any inclusion of impurity
gas in the ionized gas may cause the impurity gas molecules to desorb
near the apex of the emitter tip. The molecule desorption deforms the
shape of the emitter tip at the apex, and the electric field fluctuates
near the apex. Such electric field fluctuations cause the ion beam
current to fluctuate.

[0017] Another problem is the influence of the ion beam release from
portions where the adhesion of the impurity gas has taken place. The
portions with the adhered impurity gas project out in a size determined
by the size of the impurity gas, and involve a higher electric field than
other portions. This may cause emission of ion beams from these high
electric field portions. For every ion beam emission from the impurity
gas adsorbed portions, the ionized gas is consumed at these portions in
amounts that correspond to the ion beam emission. This reduces the supply
of ionized gas from the atom portions intended as an ion source, and
causes the ion beam current to fluctuate.

[0018] Prior to making the invention, the present inventors identified the
problem that the ion source becomes unstable for the reasons described
above.

[0019] When the impurity gas is a gas species that reacts with the metal
forming the emitter tip, the impurity gas may destroy the projection of
several atoms formed at the apex of the emitter tip. The projection at
the apex of the emitter tip needs to be reconstructed when destroyed.
This is problematic in terms of user friendliness of the device. The
present inventors found that the ease of maintaining the projection for
extended time periods depends on the type of the ionized gas used, and
the gas purity, and that these factors make it difficult to observe a
sample in high resolution.

[0020] This problem can be solved by removing the impurity gas from the
ionized gas, specifically by purifying the ionized gas. The present
inventors looked at the notably higher vapor pressures of certain ionized
gas species such as helium, neon, and hydrogen commonly used for
observation purposes than those of other gas species, and found that the
ionized gas can be efficiently purified by cooling the ionized gas.
Specifically, the ionized gas can be cooled to aggregate impurity gases
such as nitrogen, oxygen, and hydrocarbon, and introduce only the gas of
interest near the emitter tip.

[0021] It is an object of the present invention to improve the reliability
of a gas field ionization ion source at low cost by purifying an ionized
gas with a cooling system intended to cool the emitter tip and improve
the ion emission angle current density.

Solution to Problem

[0022] A representative example of the present invention is as follows. A
charged particle microscope that has a field ionization ion source
includes:

[0023] an emitter tip having a needle-like apex;

[0024] an ionization chamber having the emitter tip inside the chamber;

[0025] a first heat exchanger connected to a part of the ionization
chamber via a cooling conductor,

[0026] a cryocooler having a second heat exchanger,

[0027] a first gas line that supplies a gas to the ionization chamber via
the second heat exchanger; and

[0028] a second gas line thermally connected to the first heat exchanger
and the second heat exchanger.

Advantageous Effects of Invention

[0029] The present invention enables a stable supply of an ion beam in a
charged particles beam apparatus that irradiates a sample with an ion
beam for sample observation.

BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a diagram representing a schematic structure of an
example of the charged particles beam apparatus according to the present
invention.

[0031] FIG. 2 is a diagram representing a schematic structure of a cooling
mechanism in the example of the charged particles beam apparatus
according to the present invention.

[0032] FIG. 3 is a diagram representing a schematic structure of a cooling
mechanism in the example of the charged particles beam apparatus
according to the present invention.

[0033] FIG. 4 is a diagram representing a schematic structure of an
example of the charged particles beam apparatus according to the present
invention.

[0034] FIG. 5 is a diagram representing a schematic structure of an
example of the charged particles beam apparatus according to the present
invention.

[0035] FIG. 6 is a diagram (cross sectional view) representing a schematic
structure of a vacuum insulation pipe in the example of the charged
particles beam apparatus according to the present invention.

[0036] FIG. 7 is a diagram (cross sectional view) representing a schematic
structure of a vacuum insulation pipe in the example of the charged
particles beam apparatus according to the present invention.

DESCRIPTION OF EMBODIMENTS

[0037] The present invention is a charged particle microscope that
includes: a field ionization ion source provided with an emitter tip
having a needle-like apex, an ionization chamber containing the emitter
tip inside the chamber, a first gas line that supplies a gas into the
ionization chamber, and an extraction electrode disposed opposite the
emitter tip; a sample holder for holding a sample; and a lens group for
converging an ion beam. The charged particle microscope includes a first
heat exchanger thermally coupled to a part of the field ionization ion
source, a cryocooler capable of cooling a second gas line and a cold
head, the second gas line being connected to the first heat exchanger and
circulating a refrigerant, and a second heat exchanger connected to the
cold head that cools the first and second gas lines. This makes it
possible to efficiently purify the ionized gas supplied into the
ionization chamber. Specifically, with the structure adapted to cool the
first gas line with the second heat exchanger, the impurity gas contained
in the ionized gas running through the first gas line aggregates at the
cooled portions of the first gas line. Further, the gas can be purified
at low cost because the second heat exchanger and the cryocooler,
provided as essential components for cooling the emitter tip and
improving the brightness of the ion beam to obtain a high-resolution
observation image, are also used to cool the first gas line.

[0038] The present invention is a charged particle microscope that
includes a field ionization ion source provided with an emitter tip
having a needle-like apex, an ionization chamber containing the emitter
tip inside the chamber, a first gas line that supplies a gas into the
ionization chamber, and an extraction electrode disposed opposite the
emitter tip; a sample holder for holding a sample; and a lens group for
converging an ion beam. The charged particle microscope includes a first
heat exchanger thermally coupled to a part of the field ionization ion
source, a cryocooler capable of cooling a second gas line and a cold
head, the second gas line being connected to the first heat exchanger and
circulating a refrigerant, a second heat exchanger connected to a vacuum
chamber retaining a gas molecule supplied to the first gas line, and to
the cold head that cools the vacuum chamber and the second gas line, and
a gas flow rate adjusting mechanism provided on the first gas line
joining the gas-containing vacuum chamber and the ionization chamber. In
this way, the quantity of the purified gas that can be supplied to the
field ionization ion source can be increased. This is possible because a
large quantity of ionized gas retained in the vacuum chamber can be
purified at once with the configuration in which the cryocooler is
adapted to cool the vacuum chamber that can retain the ionized gas. This
makes it possible to stably introduce a large quantity of ionized gas to
the field ionization ion source for consumption.

[0039] With the flow rate adjusting mechanism provided on the first gas
line between the vacuum chamber and the ionization chamber, the supply of
the ionized gas to the field ionization ion source can be suspended until
the purification is finished. This enables the ionized gas to be purified
without sacrificing the reliability of the field ionization ion source.
The flow rate adjustment also enables adjusting the ionized gas pressure
inside the ionization chamber.

[0040] The present invention is a charged particle microscope that
includes a field ionization ion source, a device mount for supporting a
sample holder and a lens group, and an antivibration mechanism that
reduces the vibration of the device mount, and in which the cryocooler is
supported on a mount different from the device mount. In this way, the
emitter tip and the ionized gas can be cooled without transmitting the
vibration of the cryocooler to the emitter tip or the sample holder. By
reducing the vibration, the amplitudes of the relative vibrations of the
emitter tip and the sample become smaller, and the sample can be observed
at high resolutions.

[0041] The charged particle microscope may be adapted to include a pipe
that vacuum insulates the first and second gas lines, and in which the
outer walls of the first and second gas lines are partially or entirely
in contact with each other. In this way, the first gas line can be cooled
to about the same temperature as that of the refrigerant circulating
inside the second gas line. This makes it possible to introduce the
cooled purified ionized gas into the ionization chamber while maintaining
the purity.

[0042] The charged particle microscope may be adapted so that the
cryocooler is a Gifford-McMahon (GM) cryocooler or a pulse tube
cryocooler. This makes it easier to continuously operate the charged
particle microscope.

[0043] The charged particle microscope is adapted so that the cryocooler
is a container capable of retaining liquid nitrogen, that the liquid
nitrogen inside the container is solidifiable with the use of a means
that can lower the pressure inside the container. This makes it possible
to cool the emitter tip and the ionized gas relatively inexpensively. It
is also possible to suppress the vibration of the cryocooler.

[0044] The present invention is a charged particle microscope that
includes a field ionization ion source provided with an emitter tip
having a needle-like apex, a first gas line that supplies a gas molecule
near the emitter tip, and an extraction electrode disposed opposite the
emitter tip; a sample holder for holding a sample; and a lens group for
converging an ion beam. The charged particle microscope includes a first
heat exchanger thermally coupled to a part of the field ionization ion
source, a cryocooler capable of cooling a second gas line and a cold
head, the second gas line being connected to the first heat exchanger and
circulating a refrigerant, and a second heat exchanger connected to the
cold head that cools the second gas line. The first gas line and the
second gas line are connected to each other with a mechanism that can
adjust the flow rate, and the refrigerant circulating inside the second
gas line can be partially supplied to the ionization chamber. In this
way, for example, a gas, such as helium, neon, argon, and hydrogen, that
can be used as an ionized gas can be selected as the refrigerant that
circulates inside the second gas line, introduced into the ionization
chamber. Because the refrigerant circulating inside the second gas line
is cooled by the second heat exchanger and the cryocooler, the ionized
gas is purified by the impurity gas aggregation effect. This makes it
possible to inexpensively purify the ionized gas, and introduce the
purified ionized gas into the ionization chamber.

[0045] Referring to FIG. 1, the following describes an example of the
charged particles beam apparatus according to the present invention. An
ion beam apparatus as a first example of a scanning ion microscope is
described first. The scanning ion microscope of this example includes a
gas field ionization ion source 1, an ion beam irradiation column 2, a
sample chamber 3, and a cryogenic mechanism 4. The gas field ionization
ion source 1, the ion beam irradiation column 2, the sample chamber 3,
and the cooling mechanism 4 are vacuum chambers.

[0046] The gas field ionization ion source 1 includes a needle-like
emitter tip 11, and an extraction electrode 13 provided opposite the
emitter tip 11 and having an opening 12 through which ions pass through.
In this example, an ionization chamber outer wall 14 covers the emitter
tip 11, and forms an ionization chamber 17. However, the ionization
chamber outer wall 14 may be formed so that it shares the same outer wall
with the vacuum chamber of the gas field ionization ion source section.

[0047] The beam irradiation column 2 includes a focusing lens 21 that
focuses the ions released by the gas field ionization ion source 1; a
first aperture 22 movably provided to restrict an ion beam 15 that has
passed through the focusing lens 21; a first deflector 23 that scans or
aligns the ion beam 15 that has passed through the first aperture 22; a
second deflector 24 that deflects the ion beam 14 that has passed through
the first aperture 22; a second aperture 25 that restricts the ion beam
15 that has passed through the first aperture; and an objective lens 26
through which the ion beam 15 that has passed through the first aperture
22 and the second aperture 25 are focused on a sample 31.

[0048] Inside the sample chamber 3 are provided a sample stage 32 for
mounting the sample 31, and a secondary particle detector 33. The ion
beam 15 from the gas field ionization ion source 1 irradiates the sample
31 through the ion beam irradiation column 2. The secondary particles
from the sample 31 are detected by the secondary particle detector 33.
There are also provided an electron gun for neutralizing the charge of
the sample irradiated with the ion beam, and a gas gun for supplying a
gas near the sample, though not illustrated. The gas gun supplies gases
such as a deposition gas, and a charge neutralization gas.

[0049] The cooling mechanism 4 is a mechanism that cools various parts of
the apparatus, including inside of the field ionization ion source 1, the
emitter tip 11, the extraction electrode 12, and the ionization chamber.
When the cooling mechanism 4 uses, for example, a Gifford-McMahon (GM)
cryocooler, a compressor unit 411 (compressor) for circulating a helium
gas is installed, and is connected to a cryocooler main body 41 with a
cryogenic pipe 42. Typically, certain parts of the cryocooler main body
41 are suited for the transfer of the cooling capacity of the cryocooler
main body 41. For example, in the case of FIG. 1 using a GM cryocooler,
the portion suited for cooling is a first cold head 412 that has higher
cryogenicity than a second cold head 413 (described later), and is
coolable from relatively higher temperatures. A second cold head 413 that
has a lower cryogenicity temperature than the first cold head 412, and is
coolable to a relatively lower temperature may also represent such a
suitable cooling portion.

[0050] A first gas line 43 and a second gas line 44 are connected to the
second cold head 413 via a second heat exchanger 47. An ionized gas, such
as helium, neon, argon, and hydrogen, supplied from a gas cylinder 431 is
introduced near the emitter tip 11 through the first gas line. The
ionized gas is cooled by at least the second heat exchanger as it is
supplied from the gas cylinder 431. The first gas line 43 may be
connected to the first cold head 412, or to a part of the second gas line
via a heat exchanger other than the second heat exchanger 47. Such an
additional interconnection enables preliminary cooling of the ionized
gas, and reduces the thermal load on the cryocooler, making it possible
to cool the gas to even lower temperatures. An example of the apparatus
configuration concerning the preliminary cooling will be described later
in detail.

[0051] The heat exchanger may be one obtained by winding and welding a
refrigerant or ionized gas pipe to a material having good thermal
conductivity, for example, such as copper. Maximizing the pipe length can
improve the heat exchange efficiency, and enable a large quantity of
refrigerant or ionized gas to be cooled to even lower temperatures.
Inside the pipe of the heat exchanger may be a porous material having a
larger surface area, for example, such as sintered fine particles of
activated carbon or metal filling the pipe. Filling the pipe with such a
large-surface-area material improves the heat exchange efficiency, and
enables a large quantity of refrigerant or ionized gas to be cooled to
even lower temperatures.

[0052] The first gas line 43 and the second gas line 44 may be adapted to
evacuate with a vacuum pump (not illustrated). The vacuum pump may be,
for example, an evaporable getter pump such as a rotary pump, a scroll
pump, a turbo-molecular pump, a sputter ion pump, and a Ti sublimation,
or a non-evaporable getter pump. These devices may be used alone or in a
configuration as a combination of different devices to evacuate and
create a vacuum. The purity of the refrigerant or ionized gas can be
increased by performing preliminary evacuation with such a device
configuration before introducing the refrigerant or ionized gas.

[0053] The first gas line 43 and the second gas line 44 may be configured
to be heatable with heating means such as a heater (not illustrated).
Heating with a heater or the like during preliminary evacuation can
accelerate the desorption of the adsorbed gas inside the gas lines, and
improve the degree of vacuum inside the gas lines prior to the
introduction. That is, the purity of the ionized gas or refrigerant can
improve.

[0054] The emitter tip 11 is cooled as a refrigerant such as helium gas,
neon gas, and nitrogen gas circulates between a first heat exchanger 46
and a second heat exchanger 47 through the second gas line 44, and
transfers the cooling heat to a cooling conductor 45. A compressor unit
441 is used for the circulation of the refrigerant. The cooling conductor
45 is connected to a part of the gas field ionization ion source,
specifically, the emitter tip 11, the extraction electrode 13, or the
ionization chamber outer wall 14. The second gas line 44 may be connected
to the first cold head 412 via a heat exchanger different from the second
heat exchanger 47. The portions of the second gas line 44 where the
refrigerant is directed toward the first heat exchanger and returns from
the first heat exchanger 46 may also be connected to each other via a
heat exchanger different from the second heat exchanger 47. Such an
additional interconnection enables preliminary cooling of the
refrigerant, and reduces the thermal load on the cryocooler, making it
possible to cool the refrigerant to even lower temperatures. An example
of the apparatus configuration concerning the preliminary cooling will be
described later in detail. Preferably, the cold head is cooled to a
temperature of 70 K or less.

[0055] The scanning ion microscope of this example further includes an ion
source evacuation pump 16 that evacuates the gas field ionization ion
source 1, and a sample chamber evacuation pump 34 that evacuates the
sample chamber 3. On a device mount 6 disposed on a floor 5 is a base
plate 62 disposed via an antivibration mechanism 61. The base plate 62
supports the field ionization ion source 1, the ion beam irradiation
column 2, the sample chamber 3, and the cooling mechanism 4.

[0056] With this configuration, the impurity gas contained in the ionized
gas aggregates at the cooled portions of the first gas line, and the
ionized gas of improved purity can be constantly introduced into the
ionization chamber. Further, the gas can be purified at low cost because
the second heat exchanger 47 and the cryocooler are provided as essential
components for cooling the emitter tip and improving the brightness of
the ion beam to obtain a high-resolution observation image.

[0057] FIG. 2 represents an example in which the first gas line and the
second gas line connected to the second cold head 413 are preliminarily
cooled with the configuration of the ion microscope of the present
invention shown in FIG. 1. The first gas line is cooled with a third heat
exchanger 481 connected to the first cold head 412, and with the second
heat exchanger 47 connected to the second cold head 413. The second gas
line is cooled with the third heat exchanger 481 connected to the first
cold head 412, and with the second heat exchanger 47 connected to the
second cold head 413. In a fourth heat exchanger 482, a heat exchange
takes place between the outgoing and incoming second gas lines. With this
configuration, the thermal load on the cryocooler can be reduced, and the
emitter tip and the ionized gas can be cooled to even lower temperatures.
The GM cryocooler is used alone in the examples of FIGS. 1 and 2;
however, the present invention also encompasses use of more than one GM
cryocooler.

[0058] It should be noted, however, that a characteristic feature of the
present invention is that the first gas line 43 and the second gas line
44 are both connected to at least one heat exchanger. This configuration
enables desirably cooling the both gas lines, and supplying a high purity
ionized gas to the emitter tip 11, and makes it possible to inexpensively
provide a reliable ion microscope with the least number of cryocoolers.

[0059] FIG. 3 represents a configuration in which a container 414
retaining a refrigerant is used to cool the emitter tip and the ionized
gas instead of using the GM cryocooler. In this configuration, the second
heat exchanger is connected to the container 414 retaining a refrigerant
416. The refrigerant 416 may be, for example, liquid nitrogen, solid
nitrogen, liquid neon, or liquid helium. The first gas line and the
second gas line are connected via the second heat exchanger to the
container retaining the refrigerant, and are cooled by the latent heat of
the refrigerant 416. A evacuation pipe 415 is attached to the container
414 retaining the refrigerant 416. The container 414 retaining the
refrigerant 416 can be vacuumed with a pump (not illustrated) via the
evacuation pipe 415. The vacuuming lowers the pressure inside the
container, and can lower the temperature of the refrigerant 416 retained
therein. When the refrigerant 416 is liquid nitrogen, the vacuuming can
promote a phase transition from liquid nitrogen to solid nitrogen. The
transition from liquid to solid can reduce the apparatus vibrations
caused by boiling of the liquid nitrogen. In a scanning ion microscope,
any relative vibrations of the emitter tip and a sample cause the sample
image resolution to deteriorate. The vacuuming can reduce such sample
resolution deterioration to some extent.

[0060] Referring to FIG. 4, an example of the charged particles beam
apparatus according to the present invention is described below. This
example differs from FIG. 1 in that a vacuum chamber 432 that can retain
the ionized gas is provided on the first gas line, and the apparatus also
includes a means 434 that can adjust the flow rate of the gas inside the
first gas line joining a vacuum chamber 433 and the ionization chamber.
In this example, the first gas line from a gas cylinder 431 is connected
to the vacuum chamber 433 via a valve 433. The gas is introduced into the
ionization chamber 17 via the flow rate adjusting means 434.

[0061] This example uses a GM cryocooler. In the figure, the vacuum
chamber 433 is shown as being cooled via the second heat exchanger.
However, the vacuum chamber 433 may be configured to be directly
connected to the second cold head. The present invention also encompasses
use of more than one cryocooler. It should be noted, however, that a
characteristic feature of the present invention is that the vacuum
chamber 433 is cooled by the same cryocooler that cools the second gas
line. Specifically, at least one cryocooler simultaneously cools the
vacuum chamber 433 and the second gas line. This configuration enables
supplying a high purity ionized gas to the emitter tip 11, and makes it
possible to inexpensively provide a reliable ion microscope with the
least number of cryocoolers.

[0062] The first gas line 43 and the second gas line 44 also may be
configured to be preliminarily cooled in this example. Specifically, for
example, the apparatus may be configured so that the first gas line 43
and the second gas line 44 are cooled by the first cold head 412 before
the ionized gas running through the first gas line is retained by the
vacuum chamber 433. The second gas line may be connected to the first
cold head 412 via a heat exchanger different from the second heat
exchanger, as with the foregoing example. The portions of the second gas
line 44 where the refrigerant is directed toward the first heat exchanger
and returns from the first heat exchanger 46 also may be connected to
each other via a heat exchanger different from the second heat exchanger
47. Such an additional interconnection enables preliminary cooling of the
refrigerant, and reduces the thermal load on the cryocooler, making it
possible to cool the refrigerant to even lower temperatures.

[0063] With the ionized gas retained inside the cooled vacuum chamber 433,
the impurity gas contained in the ionized gas aggregates on the inner
wall of the vacuum chamber 433, and the purity of the ionized gas
improves. In order for the apparatus to operate with the maintained high
ion beam brightness, a high pressure needs to be maintained for the
ionized gas inside the ionization chamber. This means that there is a
need to accommodate a large consumption of high purity ionized gas for
the observation of a high-resolution image. To this end, the ionized gas
may be introduced in a preliminary stage before operating the ion
microscope. By retaining the cooled ionized gas, the thermal load on the
cryocooler can be reduced while maintaining the purity constant at all
times. A large consumption of ionized gas also can be accommodated by
increasing the ionized gas pressure inside the vacuum chamber 433 to the
required level in a preliminary stage.

[0064] The vacuum chamber 433, the first gas line 43, and the second gas
line 44 may be configured to evacuate with a vacuum pump (not
illustrated). The vacuum pump may be, for example, an evaporable getter
pump such as a rotary pump, a scroll pump, a turbo-molecular pump, a
sputter ion pump, and a Ti sublimation, or a non-evaporable getter pump.
These devices may be used alone or in a configuration as a combination of
different devices to evacuate and create a vacuum. The purity of the
refrigerant or ionized gas can be increased by performing preliminary
evacuation with such a device configuration before introducing the
refrigerant or ionized gas. The vacuum chamber 433, the first gas line
43, and the second gas line 44 may be configured to be heatable with
heating means such as a heater (not illustrated). Heating with a heater
or the like during preliminary evacuation can accelerate the desorption
of the adsorbed gas inside the gas lines, and improve the degree of
vacuum inside the gas lines prior to the introduction. That is, the
purity of the ionized gas or refrigerant can improve.

[0065] Referring to FIG. 5, an example of the charged particles beam
apparatus according to the present invention is described. In the
scanning ion microscope of this example, the cryocooler is supported on a
device mount different from the device mount supporting the scanning ion
microscope main body configured from the gas field ionization ion source
1, the ion beam irradiation column, and the sample chamber 3.
Specifically, the scanning ion microscope main body and the cooling
mechanism 4 are supported on different device mounts. The cryocooler
typically vibrates during its operation. Taking a GM cryocooler as an
example, the cryocooler main body involves piston vibrations, and becomes
a source of vibration. The compressor unit operating to circulate helium
is another source of vibration. The apparatus is also vibrated by the
bubbles that generate during the boiling of the refrigerant when a
container retaining the refrigerant is used as a cryocooler. As described
above, the relative vibrations of the emitter tip 11 and the sample 31
cause image resolution deterioration in a scanning ion microscope. By
using different device mounts to support the cryocooler and the ion
microscope main body producing vibrations, it is possible to reduce the
transmission of vibrations, the deterioration of image resolution.

[0066] Because the ion microscope main body and the cooling mechanism 4
are supported on different device mounts, the first gas line 43 and the
second gas line 44 need to be extended. Further, because the ionized gas
running through the first gas line 43 cooled by the cooling mechanism,
and the refrigerant running through the second gas line 44 are
transported to the ion microscope main body in the maintained cold state,
these gas lines need to be covered with a vacuum insulation pipe 49 to
shield an influx of external heat. The vacuum insulation pipe 49 may be
configured as a single pipe that can simultaneously vacuum insulate the
first gas line and the outgoing and incoming second gas lines. The first
gas line may be configured so that any part or all of the first gas line
from the cooling mechanism 4 to the ionization chamber is in contact with
the second gas line. With this configuration, the first gas line can be
maintained in the cooled state over a wide range.

[0067] FIG. 6 is across sectional view of the vacuum insulation pipe with
the first gas line and the second gas line. FIG. 6A illustrates the first
gas line 43 in contact with an outgoing second gas line 44A. FIG. 6B
illustrates the first gas line contained inside the outgoing second gas
line 44A.

[0068] The vacuum insulation pipe 49 may be configured so that its outer
wall has a movable bellows or accordion structure in a part of the pipe
or throughout the pipe (not illustrated). Because the vacuum insulation
pipe 49 joins the cooling mechanism 4 and the ion microscope main body
that become vibration sources, the vacuum insulation pipe 49 can transmit
the vibration of the cooling mechanism 4 to the ion microscope main body.
However, when the vacuum insulation pipe 49 is configured to have a
movable structure as above, the vibration does not easily transmit, and
the deterioration of micrograph resolution can be reduced. A part of the
vacuum insulation pipe 49 having a movable structure such as above may be
fixed to any of the device mount supporting the ion source main body, the
device mount supporting the cooling mechanism, and a third device mount
different from these device mounts. The transmission of the generated
vibration from the cryogenic mechanism 4 to the ion microscope main body
can be particularly suppressed by fixing the vacuum insulation pipe 49 to
the third device mount.

[0069] The second gas line in FIG. 5 makes one circulation between the
cryogenic mechanism 4 and the ion microscope main body. However, the
second gas line may be structured to circulate the refrigerant more than
once.

[0070] FIG. 7 is a cross sectional view of a vacuum insulation pipe
structured this way. In this example, the outgoing and incoming second
gas lines for a first circulation are disposed inside the outgoing and
incoming second gas lines provided for a second circulation. A heat
radiation shield is disposed around the inner gas lines, and the outer
second gas lines cool the heat radiation shield that is in contact with
the outer second gas lines. This structure reduces the influx of heat
into the gas lines disposed inside the heat radiation shield, and the
refrigerant and the ionized gas can be transported to the ion microscope
main body at the maintained low temperature.